Fixes for option parsing

Hi Steven,

I've made two patches for fixing issues noticed during parsing of icmpv6 options (introduced by one of my previous commits); first patch (47ee3f8) fixes issue during icmpv6 option parsing when validating the icmpv6 message while the last patch (f40d224) fixes issue in the icmpv6 option iterator macro caused by lack of valid pointer casts.

Bye,
Hans